TiNi-based wire is widely used in the manufacture of surgical implants and designs due to its biocompatibility and ability to undergo viscoelastic deformation with tissues, withstanding millions of deformation cycles without destruction. TiNi is a self-passivating material, as it forms a complex surface oxide layer that protects the material from corrosion and is itself biocompatible. The functional properties of TiNi wire are determined by the structure, composition, and thickness. The purpose of this work is to study the deformation behavior of thin TiNi wires depending on the thickness. TiNi wires of different thicknesses (40, 60, 90 µm) were tested by uniaxial tension to rupture and in the load-unload cycle (5 cycles). The results found that All TiNi wires exhibit the effect of superelasticity at a relative strain of 5-7%. With an increase in the wire thickness from 40 to 90 µm, the values of the martensitic shear stress increase from 450 to 1200 MPa and the tensile strength increases from 1300 to 3150 MPa.